In a fabrication/inspection process of functional device products manufactured through surface fine working, such as semiconductor devices and thin film magnetic heads, a scanning electron microscope is widely used for finding the size of a worked pattern width (hereinafter called “measurement”) and external appearance inspection.
The electron scanning microscope is an apparatus in which an electron beam emitted from an electron source and finely focused by means of focusing and objective lenses each utilizing an interaction of the electron beam with a magnetic or electric field is scanned one-dimensionally or two-dimensionally on a sample by using a deflector, a secondary signal generated from the sample by electron beam irradiation (secondary electrons, reflected electrons or electromagnetic waves) is detected with a detector utilizing the photoelectric effect and the detected signal is converted/processed into a visual signal such as a brightness signal synchronous with scanning of the electron beam to form a sample image.
In the scanning electron microscope, an effort is made to obtain a sample image highly accurately corresponding to the shape of a sample surface to be observed/measured and a distance between two arbitrary points on the sample surface is calculated from the thus obtained sample image. This calculation is generally called “measurement” and a scanning electron microscope having the calculation function as above is called a “measuring electron microscope”.
Needless to say, in this type of scanning electron microscope, an electron beam having an arrival energy amount of several of hundreds of electron volts is irradiated on the surface of a sample to be observed.
Meanwhile, fine working of the surface of semiconductors has been further advanced in recent years and the use of photo resist reactive to argon fluoride (ArF) excimer laser light (hereinafter called “ArF resist”) as a photolithography sensitive material has been started. The ArF laser light has a short wavelength of 160 nm and the ArF resist is therefore considered to be suitable for use in exposure of finer circuit patterns.